So-called field devices, i.e. measuring devices installed near to a process, are applied in process measurements technology, especially for automation of chemical processes and/or for automation of procedures for producing a product from a raw or starting material by the use of chemical, physical or biological processes and/or for control of industrial plants. Field devices embodied as sensors can monitor, for example, process measurement variables such as pressure, temperature, flow, fill level or measurement variables of liquid and/or gas analysis, such as, for example, pH-value, conductivity, concentrations of certain ions, chemical compounds and/or concentrations or partial pressures of gases.
Frequently, a large number of most varied sensors are used in a process installation. A sensor arranged at a certain location of installation in the process, for example, a sensor installed at a certain location and embodied for registering one or more measurement variables, forms a measuring point.
A sensor includes, as a rule, a measuring transducer, which is embodied to register the measured variable to be monitored and to produce an electrical measurement signal correlated with the current value of the measured variable. Serving today for additional processing of the measurement signal is most often an electronic, evaluation circuit, which is embodied to condition the electrical, measurement signal further, for example, to digitize it, to convert it into a measured value of the measured variable and/or into a variable derived from the measured value, and, in given cases, to output such to a superordinated unit. The evaluation circuit can perform, besides measured value formation and measured value forwarding, more extensive functions. For example, it can be embodied to perform a more extensive evaluation of the measured values or to conduct sensor diagnostics, in the case of which a current state of the sensor is determined and/or a prediction of the remaining life of the sensor occurs.
In the case of sensors of the aforementioned type, the evaluation circuit is frequently connected with a superordinated data processing system most often arranged spatially removed from the respective measuring point. Measured values produced by the respective sensor, diagnosis relevant data or other sensor data are forwarded to the superordinated data processing system. The superordinated data processing system can especially include one or more electronic process controllers, for example, one or more on-site, measurement transmitters, a process control computer or a programmable logic controller (PLC).
Frequently serving, at least sectionally, for data transmission in such industrial measuring arrangements are fieldbus systems, such as, for example, FOUNDATION Fieldbus, PROFIBUS, ModBus, etc. or, for example, also networks based on the Ethernet standard. Accompanying these fieldbus systems are the corresponding, most often application independently standardized, transmission protocols.
Known from published International Application WO 2005/031339 is a liquid sensor, which is connected via a coupling with a measurement transmitter and further with a superordinated data processing system. The sensor includes a measuring transducer and a sensor circuit, which has a preprocessing circuit for preprocessing the analog measuring signals produced by means of the measuring transducer, an analog/digital converter for converting the registered, analog, measurement signals into digital measurement signals and a first interface for transmitting the digital measurement signals to the superordinated measurement transmitter. The coupling comprises a sensor side, primary coupling element and a complementary, secondary coupling element, which is connected with the measurement transmitter. The first interface is embodied to transmit the digital measurement signals via the coupling to the measurement transmitter. The secondary coupling element includes another electronic circuit, which has, complementary to the first interface, a second interface, which is embodied to receive the measurement signals transmitted from the first interface. The second interface can, moreover, transmit data as well as energy via the coupling to the first interface of the sensor. The transmission of energy and data occurs in the case of the sensor known from published International Application WO 2005/031339 A1 contactlessly by means of an inductive coupling of the first and second interfaces. This assures also a galvanic decoupling of the sensor from the measurement transmitter.
Measurement transmitters conventionally have display means, e.g. a display, and input means, e.g. in the form of a keyboard or one or more rotate/press switches, by means of which a user can read measured values and sensor data, respectively input parameters or commands.
In earlier times, measuring arrangements existed, which did without a conventional measurement transmitter having input and display means. Described in German Patent DE 10 2011 107 717 A1 is a sensor for liquid or/and gas analysis, which is connected with a measuring or/and evaluation circuit, respectively with a superordinated control system. The sensor includes a sensor housing, in which are provided circuit means for registering, conditioning and forwarding measured values to the measuring- or/and evaluation circuit, respectively to the control system. This circuit means comprises an analog sensor electronics, an analog/digital converter for converting the registered analog, measured values into digital, measured values, a computing unit and communication means for conditioning and forwarding the digital measured values to the measuring or/and evaluation circuit, respectively to the control system, using a standard communication protocol of process technology, for example, HART, PROFIBUS PA, PROFIBUS DB or Foundation Fieldbus. Goal of the sensor construction illustrated in German Patent DE 102011107717 A1 is to integrate as much electronics as possible into the sensor. Thus the sensor electronics arranged in the sensor housing is embodied not only for registering and, in given cases, digitizing the measured values registered by a measuring transducer of the sensor but also for additional processing and conversion of the measured values into a standard communication protocol processable by the control station.
Sensors for liquid and/or gas analysis must, during their lifetime, as a rule, from time to time, undergo maintenance, especially be calibrated or regenerated. To this end, frequently the sensor to be maintained is removed from the measuring point and the maintenance measure performed at another location, for example, in the laboratory. In the intervening time, the measuring point can be operated further with another sensor of the same type. The lifetime of sensors for liquid and/or gas analysis is, moreover, limited and depends on the particular features of the measuring point. Lifetime can lie, for example, between a few days and some months. This leads to the fact that the sensors of a measuring point must regularly be replaced. A disadvantage of a measuring arrangement, in the case of which as much electronics as possible is accommodated in the sensor, is, thus, that, in the case of each sensor replacement, not only data stored in the sensor, but, instead, also measuring point specifically matched parameters and measuring location specific program code get removed from the measuring point. These parameters, respectively program code, must be provided anew to the replacement sensor. Moreover, the lifetime of the components of a sensor electronics is clearly longer than the usual lifetime of the measuring transducer of the sensor. It is, consequently, uneconomic to replace these components with the same frequency as the measuring transducer.
European Patent EP 2 233 994 A2 describes a measuring arrangement, which includes an intelligent, process sensor, which is connectable releasably with an electronics module. The electronics module includes a microprocessor with a memory unit, a plurality of digital interfaces and a means for forwarding analog signals from the process sensor to a process control system. The process sensor serves for determining at least one chemical or physical, measured variable of a measured medium and includes, besides a measuring transducer for registering the measured variable, an electronics unit connected inseparably with the measuring transducer. The electronics unit comprises a means for monitoring the sensor state, a means for digitizing the analog measurement data from the sensor unit, a means for forwarding the analog and digitized data, at least one analog interface and at least one digital interface for connection of the process sensor with the process control system, and a galvanic isolation between the measured medium and the interfaces. The electronics unit connected inseparably with the measuring transducer serves to process measurement data, to monitor the sensor state and to store the sensor relevant data. In general, it performs, thus, functions of an otherwise usual measurement transmitter in the field of analytical measurements technology. The electronics module serves to output the data and diagnostic information provided by the intelligent sensor via one or more interfaces, for example, to a process control system or to a mobile servicing device using a communication protocol processable by the process control system, respectively by the mobile servicing device. Since also here essential measurement transmitter functionalities are provided by an electronics inseparably connected with the measuring transducer, the measuring arrangement known from European Patent EP 2 233 994 A2 has essentially the same disadvantages as the apparatus described in German Patent DE 10 2011 107 717 A1.